1. Field of the Invention
The present invention relates generally to self-cleaning appliances, and more particularly to photocatalytically-activated self-cleaning appliances and methods of making and using such appliances.
2. Description of the Related Art
Various major household appliances, such as conventional gas or electric ovens, microwave ovens, toaster ovens, refrigerators, freezers, dishwashers, clothes washers, clothes dryers, to name a few, require frequent cleaning to remove organic contaminants that have accumulated on various internal and external surfaces of such appliances. Generally this is done manually by application of various cleansers and detergents, often accompanied by scrubbing and wiping.
To avoid such manual cleaning, some self-cleaning appliances, particularly ovens, are presently available. Self-cleaning ovens clean only the interior surfaces of the oven's cooking chamber by heating the oven's cooking chamber to very high temperatures for extended periods of time to burn off organic food residues on the surfaces of the oven's cooking chamber.
Several disadvantages are attendant with such self-cleaning appliances. One disadvantage is the substantial cost of the energy needed to raise and maintain the appliance at self-cleaning temperatures. For example, non-self cleaning ovens operate at a maximum temperature of about 260.degree. C. (500.degree. F.), whereas a self-cleaning oven during the self-cleaning operation operates at temperatures above 649.degree. C. (1200.degree. F.). Other disadvantages include the increased cost associated with equipping such appliances to withstand the high cleaning temperatures, and the deleterious effect of such high temperatures on the appliance itself over time. Another disadvantage is that high temperature self-cleaning is usually limited to internal cooking surfaces.
Methods of removing organic contaminants from surfaces which do not require the high temperatures are available. More particularly, titanium dioxide can provide a photocatalytically-activated self-cleaning (hereinafter "PASC") surface on a substrate. Publications directed to the formation of a titanium dioxide PASC coating on a glass substrate include U.S. Pat. No. 5,595,813 and "Photooxidative Self-cleaning Transparent Titanium Dioxide Films on Glass", Paz et al., J. Mater, Res., Vol. 10, No. 11, pp. 2842-48 (November 1995). Further, a bibliography of patents and articles relating generally to the photocatalytic oxidation of organic compounds is reported in Bibliography of Work On The Photocatalytic Removal of Hazardous Compounds from Water and Air, D. Blake, National Renewable Energy Laboratory (May 1994) and in an October 1995 update and an October 1996 update.
U.S. Pat. No. 5,308,458 to Urwin et al. discloses a process for the decomposition of photocatalytically degradable organic material which includes exposing to ultraviolet light an organic material in fluid form present on the surface of a disk, which disk is coated with an anatase titanium dioxide film. The disk rotates to move the organic material radially outward across the surface of the disk.
U.S. Pat. Nos. 5,256,616; 5,194,161 and 4,997,576, all to Heller et al. disclose materials and methods for the photocatalytic oxidation of organic compounds on water. Heller discloses floating beads coated with titanium dioxide to oxidize organic compounds floating on water, such as for example, an oil spill.
Despite the recognition in the art of PASC coating, there is no disclosure of the use of such materials to produce a PASC appliance that would eliminate the drawback of manually cleaning appliances or of presently available self-cleaning appliances.